U.S. patent application number 11/089614 was filed with the patent office on 2006-09-28 for augmenter swirler pilot.
Invention is credited to John Michael Koshoffer.
Application Number | 20060213180 11/089614 |
Document ID | / |
Family ID | 36649110 |
Filed Date | 2006-09-28 |
United States Patent
Application |
20060213180 |
Kind Code |
A1 |
Koshoffer; John Michael |
September 28, 2006 |
Augmenter swirler pilot
Abstract
A turbofan gas turbine engine augmenter includes a fuel/air
swirler disposed between an axially extending bypass flowpath and
an axially extending exhaust flowpath. A swirler inlet is axially
open to and positioned substantially normal to the bypass flowpath
and a swirler outlet is open to and positioned substantially
parallel to the exhaust flowpath. A swirl chamber within the
fuel/air swirler is between the swirler inlet and the swirler
outlet. A swirl axis of the fuel/air swirler extends through the
swirler outlet substantially normal to the exhaust flowpath. An air
swirler may be centered about the swirl axis within the fuel/air
swirler. The air swirler may be a louvered or have a plurality of
swirling vanes. The swirler inlet may be radially offset with
respect to the swirl axis. An air scoop may lead from the swirler
inlet to a rounded swirler housing within which the air swirler is
disposed.
Inventors: |
Koshoffer; John Michael;
(Cincinnati, OH) |
Correspondence
Address: |
Steven J. Rosen;Patent Attorney
4729 Cornell Road
Cincinnati
OH
45241
US
|
Family ID: |
36649110 |
Appl. No.: |
11/089614 |
Filed: |
March 25, 2005 |
Current U.S.
Class: |
60/226.1 ;
60/761 |
Current CPC
Class: |
F02K 3/10 20130101; Y02T
50/60 20130101; F23R 3/20 20130101; F23R 3/14 20130101; Y02T 50/675
20130101 |
Class at
Publication: |
060/226.1 ;
060/761 |
International
Class: |
F02K 3/04 20060101
F02K003/04; F02K 3/10 20060101 F02K003/10 |
Claims
1. A turbofan gas turbine engine augmenter comprising: a fuel/air
swirler disposed between an axially extending bypass flowpath and
an axially extending exhaust flowpath, the fuel/air swirler
including a swirler inlet axially open to and positioned
substantially normal to the bypass flowpath, the fuel/air swirler
including a swirler outlet open to and positioned substantially
parallel to the exhaust flowpath, a swirl chamber within the
fuel/air swirler operably disposed between the swirler inlet and
the swirler outlet, and a swirl axis of the fuel/air swirler
extending through the swirler outlet and substantially normal to
the exhaust flowpath.
2. An augmenter according to claim 1 further comprising an air
swirler within the fuel/air swirler.
3. An augmenter according to claim 2 further comprising the air
swirler being centered about the swirl axis within the fuel/air
swirler.
4. An augmenter according to claim 2 further comprising the air
swirler being a louvered swirler.
5. An augmenter according to claim 2 further comprising the air
swirler having a plurality of swirling vanes.
6. An augmenter according to claim 2 further comprising the swirler
inlet being radially offset with respect to the swirl axis.
7. An augmenter according to claim 6 further comprising: the
fuel/air swirler having an air scoop leading from the swirler inlet
to a rounded swirler housing of the fuel/air swirler, the air
swirler being disposed within the rounded swirler housing, the air
scoop having a swirler inlet sidewall extending from the swirler
inlet to the swirler housing, and the swirler inlet sidewall being
substantially tangentially attached to the swirler housing.
8. An augmenter according to claim 7 further comprising the air
swirler being centered about the swirl axis within the fuel/air
swirler.
9. An augmenter according to claim 7 further comprising the air
swirler being a louvered swirler.
10. An augmenter according to claim 7 further comprising the air
swirler having a plurality of swirling vanes.
11. An augmenter according to claim 2 further comprising: a swirler
housing surrounding the air swirler, the swirler inlet leading into
the swirler housing and the swirler outlet leading out from the
swirler housing, and a fuel injector disposed through the swirler
housing and operably positioned to inject fuel into the swirl
chamber.
12. An augmenter according to claim 11 further comprising an
igniter disposed through the swirler housing and operably
positioned for igniting fuel injected into the swirl chamber.
13. An augmenter according to claim 12 further comprising the air
swirler being a louvered swirler centered about the swirl axis
within the swirl chamber.
14. An augmenter according to claim 13 further comprising the
swirler inlet being radially offset with respect to the swirl
axis.
15. An augmenter according to claim 14 further comprising: the
swirler housing being a rounded swirler housing, the fuel/air
swirler having an air scoop leading from the swirler inlet to a
rounded swirler housing of the fuel/air swirler, the air swirler
being disposed within the rounded swirler housing, the swirler
inlet sidewall being substantially tangentially attached to the
swirler housing.
16. An augmenter according to claim 2 further comprising: the air
swirler including a swirler cup, a swirler housing surrounding the
swirler cup, the swirler inlet leading into the swirler housing and
the swirler outlet leading out from the swirler housing, and a fuel
injector disposed through the swirler housing and operably
positioned to inject fuel into the swirl chamber.
17. An augmenter according to claim 16 further comprising an
igniter disposed through the swirler housing and operably
positioned for igniting fuel injected into the swirl chamber.
18. An augmenter according to claim 17 further comprising the
swirler cup being louvered or having swirling vanes and centered
about the swirl axis within the swirl chamber.
19. An augmenter according to claim 18 further comprising the
swirler inlet being radially offset with respect to the swirl
axis.
20. An augmenter according to claim 19 further comprising: the
swirler housing being a rounded swirler housing, the fuel/air
swirler having an air scoop leading from the swirler inlet to a
rounded swirler housing of the fuel/air swirler, the air swirler
being disposed within the rounded swirler housing, the air scoop
having a swirler inlet sidewall extending from the swirler inlet to
the swirler housing, and the swirler inlet sidewall being
substantially tangentially attached to the swirler housing.
21. An augmenter according to claim 16 further comprising the
swirler cup having a tilted or chamfered edge.
22. An augmenter according to claim 1 further comprising a means
for injecting fuel into the exhaust flowpath for combustion in a
combustion zone downstream of the fuel/air swirler.
23. An augmenter according to claim 22 further comprising a
plurality of circumferentially spaced apart radial flameholders
extending radially across the combustion zone downstream of the
fuel/air swirler.
24. An augmenter according to claim 23 further comprising a step
ring flameholder located in a radially outer portion of the
combustion zone downstream of the radial flameholders and including
an aft-facing annular radial wall attached to an axial wall.
25. An augmenter according to claim 24 further comprising the means
for injecting fuel including a plurality of first fuel
spraybars.
26. An augmenter according to claim 25 further comprising each of
the first fuel spraybars disposed within a corresponding one of the
radial flameholders.
27. A turbofan gas turbine engine augmenter comprising: a mixer
disposed between an axially extending bypass flowpath and an
axially extending exhaust flowpath and including a plurality of
tubular injector chutes extending radially inwardly from the bypass
flowpath to the exhaust flowpath, circumferentially spaced apart
radial flameholders extending radially inwardly into the and the
exhaust flowpath downstream of the injector chutes, a fuel/air
swirler disposed upstream of radial flameholders between the bypass
flowpath and the exhaust flowpath, the fuel/air swirler including a
swirler inlet axially open to and positioned substantially normal
to the bypass flowpath, the fuel/air swirler including a swirler
outlet open to and positioned substantially parallel to the exhaust
flowpath, a swirl chamber within the fuel/air swirler operably
disposed between the swirler inlet and the swirler outlet, and a
swirl axis of the fuel/air swirler extending through the swirler
outlet and substantially normal to the exhaust flowpath.
28. An augmenter according to claim 27 further comprising: the
mixer having an annular mixer wall disposed between the axially
extending bypass flowpath and the axially extending exhaust
flowpath, the tubular injector chutes being attached to the mixer
wall and extending radially inwardly into the exhaust flowpath, and
the fuel/air swirler being mounted to the mixer wall and
circumferentially located between a pair of the tubular injector
chutes.
29. An augmenter according to claim 28 further comprising an air
swirler centered about the swirl axis within the fuel/air
swirler.
30. An augmenter according to claim 29 further comprising the air
swirler being a louvered swirler.
31. An augmenter according to claim 29 further comprising the
swirler inlet being radially offset with respect to the swirl
axis.
32. An augmenter according to claim 31 further comprising: the
fuel/air swirler having an air scoop leading from the swirler inlet
to a rounded swirler housing of the fuel/air swirler, the air
swirler being disposed within the rounded swirler housing, the air
scoop having a swirler inlet sidewall extending from the swirler
inlet to the swirler housing, and the swirler inlet sidewall being
substantially tangentially attached to the swirler housing.
33. An augmenter according to claim 27 further comprising a means
for injecting fuel into the exhaust flowpath for combustion in a
combustion zone downstream of the fuel/air swirler.
34. An augmenter according to claim 33 further comprising a
plurality of circumferentially spaced apart radial flameholders
extending radially across the combustion zone downstream of the
fuel/air swirler.
35. An augmenter according to claim 34 further comprising a step
ring flameholder located in a radially outer portion of the
combustion zone downstream of the radial flameholders and including
an aft-facing annular radial wall attached to an axial wall.
36. An augmenter according to claim 35 further comprising the means
for injecting fuel including a plurality of first fuel
spraybars.
37. An augmenter according to claim 36 further comprising each of
the first fuel spraybars disposed within a corresponding one of the
radial flameholders.
38. An augmenter according to claim 28 further comprising: the air
swirler including a swirler cup, a swirler housing surrounding the
swirler cup, the swirler inlet leading into the swirler housing and
the swirler outlet leading out from the swirler housing, and a fuel
injector disposed through the swirler housing and operably
positioned to inject fuel into the swirl chamber.
39. An augmenter according to claim 30 further comprising the
swirler cup having a tilted or chamfered edge.
40. An augmenter according to claim 39 further comprising the mixer
wall having a rounded lip aft of and at least in the vicinity of
the swirler cup.
41. An augmenter according to claim 40 further comprising the
swirler cup being louvered or having swirling vanes and centered
about the swirl axis within the swirl chamber.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to aircraft gas
turbine engine augmenters and, more specifically, to augmenter
pilots.
[0002] High performance military aircraft typically include a
turbofan gas turbine engine having an afterburner or augmenter for
providing additional thrust when desired. The turbofan engine
includes, in serial flow communication, a multistage fan, a
multistage compressor, a combustor, a high pressure turbine
powering the compressor, and a low pressure turbine powering the
fan. During operation, air is compressed in turn through the fan
and compressor and mixed with fuel in the combustor and ignited for
generating hot combustion gases which flow downstream through the
turbine stages which extract energy therefrom. The hot core gases
are then discharged into an augmenter from which they are
discharged from the engine through a variable area exhaust
nozzle.
[0003] The augmenter includes an exhaust casing and liner therein
which defines a combustion zone. Fuel spraybars and flameholders
are mounted between the turbines and the exhaust liner for
injecting additional fuel when desired during reheat, thrust
augmentation, or afterburning operation for burning in the
augmenter combustor for producing additional thrust.
[0004] In a bypass turbofan engine, an annular bypass duct extends
from the fan to the augmenter for bypassing a portion of the fan
air around the core engine to the augmenter which bypass air is
used in part for cooling the exhaust liner. The bypass air must
also be efficiently mixed with the core gases prior to discharge
through the exhaust nozzle. This is typically accomplished using a
convoluted daisy mixer having circumferentially alternating hot and
cold chutes which respectively channel the core gases and bypass
air therethrough in radially outward and inward paths for mixing at
the exit plane thereof.
[0005] Various types of flameholders are known and typically
include radial and circumferential V-shaped gutters which provide
stagnation regions there behind of local low velocity regions in
the otherwise high velocity core gases for sustaining combustion
during reheat operation. Augmenter operation includes fuel
injection into an augmenter combustion zone and ignition is
initiated by some type of spark discharge or other igniter or
auto-ignition dues to hot core gases. Since the rate of gas flow
through an augmenter is normally much greater than the rate of
flame propagation in the flowing gas, some means for stabilizing
the flame is usually provided, else the flame will simply blow out
the rear of the engine, and new fuel being injected will not be
ignited.
[0006] Typically, flameholders are used for flame stabilization. In
regions where the gas flow is partially recirculated and the
velocity is less than the rate of flame propagation, there will be
a stable flame existing which can ignite new fuel as it passes.
Unfortunately, flameholders in the gas stream inherently cause flow
losses and reduced engine efficiency.
[0007] Since the core gases are the product of combustion in the
core engine, they are initially hot, and are further heated when
combusted with the bypass air and additional fuel during reheat
operation. The mixing of the core gases with the bypass air results
in cooling of the core gases. Augmenters require an ignition source
in the cases where the core gas conditions are not conducive to
reliable auto-ignition so pilots are used to start and maintain
combustion in the afterburner. One potential problem with an
afterburner is that, at some flight conditions, its pilot stage may
not light due to an excessively lean fuel-air ratio in the vicinity
of the igniters. A second problem is that the time in an operating
pilot stage may blow out when the aircraft fuel system supplies
fuel to pilot spray rings or bars. This latter problem occurs
because the fuel pressure in the pilot spray ring momentarily
diminishes as the aircraft fuel system initially attempts to supply
both the pilot spray ring and the auxiliary spray rings. As a
result, the fuel-air ratio becomes too lean to sustain combustion
of the pilot flame.
[0008] Thus, it is highly desirable to have an augmenter or
afterburner that can produce a stable flame and have reliable
ignition for igniting thrust augmenting fuel while holding down
flow losses and attendant reductions in engine performance and fuel
efficiency.
SUMMARY OF THE INVENTION
[0009] A turbofan gas turbine engine augmenter includes a fuel/air
swirler disposed between an axially extending bypass flowpath and
an axially extending exhaust flowpath. The fuel/air swirler
includes a swirler inlet axially open to and positioned
substantially normal to the bypass flowpath and a swirler outlet
open to and positioned substantially parallel to the exhaust
flowpath. A swirl chamber within the fuel/air swirler is operably
disposed between the swirler inlet and the swirler outlet. A swirl
axis of the fuel/air swirler extends through the swirler outlet and
is substantially normal to the exhaust flowpath. An exemplary
embodiment of the augmenter further includes an air swirler within
the fuel/air swirler centered about the swirl axis within the
fuel/air swirler. The air swirler may be louvered or have a
plurality of swirling vanes. The swirler inlet is radially offset
with respect to the swirl axis.
[0010] An exemplary embodiment of the fuel/air swirler includes an
air scoop leading from the swirler inlet to a rounded swirler
housing. The air swirler is disposed within the rounded swirler
housing. The air scoop has a swirler inlet sidewall extending from
the swirler inlet to the swirler housing and the swirler inlet
sidewall is substantially tangentially attached to the swirler
housing. The air scoop may be designed with some inlet
pre-diffusion with, for example, a 15% inlet pre-diffusion. An
exemplary embodiment of the air swirler is a swirler cup which may
be louvered or have a plurality of swirling vanes.
[0011] The exemplary embodiment of the augmenter includes a fuel
injector and an igniter disposed through the swirler housing and a
means for injecting fuel into the exhaust flowpath for combustion
in a combustion zone downstream of the fuel/air swirler. A
plurality of circumferentially spaced apart radial flameholders
extend radially across the combustion zone downstream of the
fuel/air swirler. A step ring flameholder is located in a radially
outer portion of the combustion zone downstream of the radial
flameholders and has an aft-facing annular radial wall attached to
an axial wall. The means for injecting fuel may include a plurality
of first fuel spraybars of which each of the first fuel spraybars
may be disposed within a corresponding one of the radial
flameholders.
[0012] The exemplary embodiment of the augmenter further includes a
mixer between the axially extending bypass flowpath and axially
extending exhaust flowpath and having a plurality of tubular
injector chutes extending radially inwardly from the mixer into the
exhaust flowpath. The radial flameholders extend radially inwardly
from an annular mixer wall of the mixer into the exhaust flowpath
downstream of the injector chutes. The fuel/air swirler is mounted
to the mixer wall upstream of radial flameholders and may be
circumferentially located between a pair of the tubular injector
chutes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The invention, in accordance with preferred and exemplary
embodiments, together with further objects and advantages thereof,
is more particularly described in the following detailed
description taken in conjunction with the accompanying drawings in
which:
[0014] FIG. 1 is an axial sectional view illustration through an
exemplary turbofan gas turbine engine having an augmenter swirler
pilot augmenter with a fuel/air swirler.
[0015] FIG. 2 is an enlarged axial sectional view illustration of
the fuel/air swirler illustrated in FIG. 1.
[0016] FIG. 3 is an aft-facing forward radial elevational view
illustration of a portion of the augmenter illustrated in FIG. 1
and taken along line 3-3.
[0017] FIG. 4 is an axial sectional view illustration through an
exemplary injector chute of the augmenter illustrated in FIG. 3 and
taken generally along line 4-4 in FIG. 3.
[0018] FIG. 5 is a radially inwardly facing partly sectional view
illustration through the exemplary fuel/air swirler illustrated in
FIG. 2.
[0019] FIG. 6 is a circumferentially facing partly sectional view
illustration through the exemplary fuel/air swirler illustrated in
FIG. 2.
[0020] FIG. 7 is a radially inwardly looking perspective view
illustration of a mixer upon which is mounted the exemplary
fuel/air swirler illustrated in FIG. 2.
[0021] FIG. 8 is an axially aftwardly facing sectional view
illustration of the exemplary fuel/air swirler illustrated in FIG.
6 and taken generally along line 8-8 in FIG. 6.
[0022] FIG. 9 is an enlarged axial sectional view illustration of
the fuel/air swirler illustrated in FIG. 1 with a swirler cup
having a tilted edge.
[0023] FIG. 10 is an enlarged axial sectional view illustration of
the fuel/air swirler illustrated in FIG. 1 with a swirler cup
having a chamfered edge.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Illustrated in FIG. 1 is an exemplary medium bypass ratio
turbofan gas turbine engine 10 for powering an aircraft (not shown)
in flight. The engine 10 is axisymmetrical about a longitudinal or
axial centerline axis 12 and has a fan section 14 upstream of a
core engine 13. The core engine 13 includes, in serial downstream
flow communication, a multistage axial high pressure compressor 16,
an annular combustor 18, and a high pressure turbine 20 suitably
joined to the high pressure compressor 16 by a high pressure drive
shaft 17. Downstream of the core engine 13 is a multistage low
pressure turbine 22 suitably joined to the fan section 14 by a low
pressure drive shaft 19. The core engine 13 is contained within a
core engine casing 23 and an annular bypass duct 24 containing a
bypass flowpath 25 circumscribed about the core engine 13. An
engine casing 21 circumscribes the bypass duct 24 which extends
from the fan section 14 downstream past the low pressure turbine
22.
[0025] Engine air enters the engine through an engine inlet 11 and
is initially pressurized as it flows downstream through the fan
section 14 with an inner portion thereof referred to as core engine
air 37 flowing through the high pressure compressor 16 for further
compression. An outer portion of the engine air is referred to as
bypass air 26 and is directed to bypass the core engine 13 and flow
through the bypass duct 24. The core engine air is suitably mixed
with fuel by fuel injectors 32 and carburetors in the combustor 18
and ignited for generating hot combustion gases which flow through
the turbines 20, 22. The hot combustion gases are discharged
through an annular core outlet 30 as core gases 28 into an exhaust
flowpath 128 extending downstream and aftwardly of the turbines 20,
22 and through a diffuser 29 which is aft and downstream of the
turbines 20, 22 in the engine 10.
[0026] The diffuser 29 includes a diffuser duct 33 circumscribed by
an annular radially outer diffuser liner 46 and is used to decrease
the velocity of the core gases 28 as they enter an augmenter 34 of
the engine. A converging centerbody 48 extending aft from the core
outlet 30 and partially into the augmenter 34 radially inwardly
bounds the diffuser duct 33. The diffuser 29 is axially spaced
apart upstream or forwardly of a forward end 35 of a combustion
liner 40 inside the exhaust casing 36. A bypass duct outlet 27 for
passing the bypass air 26 from the bypass duct 24 into the exhaust
flowpath 128 and the combustion zone 44 located between the annular
diffuser liner 46 and the casing 36. Thus, the combustion zone 44
is located radially inwardly from the bypass duct 24 and downstream
and aft of the bypass duct outlet 27.
[0027] Referring to FIGS. 1-4, 7, and the bypass duct 24 includes
an annular bypass duct outlet 27 for respectively discharging the
core gases 28 downstream into an exhaust section 126 of the engine
10. A mixer 31 disposed in the annular bypass duct outlet 27
includes a plurality of tubular injector chutes 58 extending
radially inwardly into the exhaust flowpath 128 from the diffusion
liner 46. The diffusion liner 46 is illustrated herein as an
integral part of the mixer 31 and serves as an annular mixer wall
100 of the mixer 31 from which the injector chutes 58 extending
radially inwardly into the diffuser duct 33 which is part of the
exhaust flowpath 128. The injector chutes 58 are spaced
circumferentially apart between respective pairs of a plurality of
circumferentially spaced apart radial flameholders 52. Each
injector chute 58 has an inlet 158 co-extensive with the diffusion
liner 46 for receiving the bypass air 26 therefrom, and an outlet
159 at an opposite longitudinal or axial end for injecting some of
the bypass air 26 into the core gases 28 for mixing in the
combustion zone 44. The exhaust section 126 includes an annular
exhaust casing 36 disposed co-axially with and suitably attached to
the corresponding engine casing 21 and surrounding the exhaust
flowpath 128.
[0028] Mounted to the aft end of the exhaust casing 36 is a
conventional variable area converging-diverging exhaust nozzle 38
through which the bypass air 26 and core gases 28 are discharged
during operation. The exhaust section 126 further includes an
annular exhaust combustion liner 40 spaced radially inwardly from
the exhaust casing 36 to define therebetween an annular cooling
duct 42 disposed in flow communication with the bypass duct 24 for
receiving therefrom a portion of the bypass air 26. An exhaust
section combustion zone 44 within the exhaust flowpath 128 is
located radially inwardly from the liner 40 and the bypass duct 24
and downstream or aft of the core engine 13 and the low pressure
turbine 22.
[0029] For the purposes of this patent, the augmenter 34 includes
elements in the engine 10 extending aft of the turbines 20, 22 to
the exhaust nozzle 38 as illustrated in FIGS. 1-3. The exemplary
embodiment of the augmenter 34 illustrated herein includes a
circumferential or step ring flameholder 50 at the outer diameter
of the augmenter 34 for maximizing the effective flameholding area
thereof. The step ring flameholder 50 is located in a radially
outer portion 122 of the combustion zone 44 downstream of the
radial flameholders 52 and has an aft-facing annular radial wall 47
attached to an axial wall 49. The aft-facing annular radial wall 47
axially adjoins the diffuser liner 46 and may be formed integrally
therewith at the aft end thereof. The step ring flameholder 50 in
axial section, as illustrated in FIG. 2, is in the form of an
aft-facing step which defines a recirculation zone 57 providing a
stagnation region for effecting flameholding capability
thereat.
[0030] The exemplary embodiment of the augmenter 34 illustrated
herein includes the plurality of circumferentially spaced apart
radial flameholders 52 extending radially inwardly from the
diffusion liner 46 into the exhaust flowpath 128 forward or
upstream of the step ring flameholder 50. Each radial flameholder
52 includes one or more integral first fuel spraybars 51. The
individual spraybars 51 are suitably joined in flow communication
with a conventional fuel supply 56 which is effective for
channeling fuel 45 to each of the spraybars for injecting the fuel
45 into the core gases 28 which flow into the combustion zone
44.
[0031] The step ring flameholder 50, radial flameholders 52, and
injector chutes 58 collectively provide enhanced performance of the
augmenter 34 while improving durability and effective life thereof.
The individual radial flameholders 52 provide flameholding
capability in conjunction with the step ring flameholder 50
disposed at the radially outer ends thereof which maximizes
flameholding capability, efficiency, and performance. The augmenter
34 is effective for use in medium to high bypass ratio engines 10
which have relatively large fan discharge flowrates through the
augmenter 34.
[0032] The injector chutes 58 are used to channel the bypass air
26, as shown in FIGS. 3 and 4, radially inwardly toward the
centerline of the engine for both effective mixing with the core
gases 28 needed for dry performance, and for isolating the
relatively cold bypass air 26 away from the relatively hot
recirculation zone 57 of the step ring flameholder 50 during reheat
operation for promoting combustion stability. The injector chutes
58 are spaced radially inwardly of the step ring flameholder 50 at
the radial wall 47 thereof to define a radial buffer zone 60. The
buffer zone 60 at each of the chutes 58 allows the core gases 28 to
reattach axially therein directly below the step ring flameholder
50 for promoting combustion stability and maintaining a more
uniform hot core gas temperature around the inner circumference of
the ring flameholder.
[0033] The individual chutes 58 are interposed between adjacent
radial flameholders 52. The hot core gases 28 flow axially around
each of the radial flameholders 52 and chutes 58. The core gases 28
therefore bound the inboard side of the step ring flameholder 50.
By spacing the chute outlets 159 radially inwardly below the step
ring flameholder 50 and the recirculation zone 57, the bypass air
26 is injected into the combustion zone 44 radially inwardly of the
buffer zone 60 to promote combustion stability in the step ring
flameholder 50, and reduce circumferential temperature
gradients.
[0034] In this way, a more uniform circumferential temperature
distribution of the step ring flameholder 50 may be maintained in
operation, during both dry and reheat operation, for improving the
durability and useful life of the step ring flameholder 50. The
chutes 58 channel the bypass air 26 more closely to the centerline
of the engine for improving mixing effectiveness with the core
gases 28. And most significantly, the relatively cold bypass air 26
is isolated from the recirculation zone 57 of the step ring
flameholder 50 improving performance thereof, and improving
combustion stability especially during initial ignition and
propagation of the flame during reheat operation.
[0035] Each of the injector chutes 58 is illustrated as having an
aerodynamically streamlined airfoil or teardrop-shaped for allowing
the core gases 28 to reattach or rejoin in the buffer zones 60
inwardly of the step ring flameholder 50. Each of the injector
chutes 58 is teardrop-shaped both axially and radially, with a
minimum profile at the buffer zone 60 for improving circumferential
flow uniformity of the core gases 28 below the step ring
flameholder 50. Both the inlet 158 and outlet 159 of the chutes 58
are also generally teardrop-shaped in section.
[0036] Referring to FIG. 2, since the inboard side of the step ring
flameholder 50 is directly subject to the hot core gases 28 flowing
through the combustion zone 44, the step ring flameholder 50 is
preferably cooled on its backside or radially outer surfaces. The
step ring flameholder axial wall 49 is spaced radially inwardly
from the combustion liner 40 to define a ring duct 59 for
discharging the bypass air 26 into the combustion zone 44 along the
inner surface of the combustion liner 40. In this way, the bypass
air 26 flows over the backside of the step ring flameholder 50 for
providing effective backside cooling thereof, and is then
discharged along the inner surface of the combustion liner 40. The
combustion liner 40 itself is also backside cooled, and may
otherwise include conventional cooling features such as additional
film cooling holes therethrough provided along the entire axial
extent of the combustion liner 40.
[0037] Various locations are provided for the injection of fuel
into the combustion zone 44 during reheat operation of the
augmenter 34, as illustrated in FIGS. 2, 3, and 4. A plurality of
second fuel spraybars 53 extending radially inwardly through
respective ones of the injector chutes 58 for injecting fuel into
the bypass air channeled therethrough. Each chute 58 may have one
or more of the second fuel spraybars 53 extending therein for
injecting the fuel 45 into the bypass air 26 inside each of the
chutes 58. In the exemplary embodiment illustrated herein, two of
the second fuel spraybars 53 also extend in part radially inwardly
of each of the injector chutes 58, and are surrounded by a suitable
heat shield, for additionally injecting the fuel 45 into the core
gases 28 flowing into the combustion zone 44.
[0038] As illustrated in FIGS. 2, 3, and 4, a plurality of
circumferentially spaced apart third fuel spraybars 54 extend
radially inwardly through the step ring flameholder 50 for
injecting fuel aft of the radial wall 47 thereof and into the
recirculation zone 57 fed by the core gases 28 flowable thereat. A
plurality of circumferentially spaced apart fourth fuel spraybars
71 extend radially inwardly into the step ring duct 59 for
injecting fuel therein to mix with the bypass air 26 flowable
therethrough. In this way, air flowing through the ring duct 59 is
fueled during reheat operation and discharged into the combustion
zone 44.
[0039] The step ring flameholder 50 effectively cooperates with the
individual radial flameholders 52 for circumferentially propagating
the flame between the radial flameholders 52 during initial
ignition, conventionally provided in the step ring flameholder 50,
and during propagation, as well as collectively providing therewith
an efficient flameholder surface area for enhanced combustion
stability during reheat operation. The embodiment of the radial
flameholders 52 illustrated herein includes the first fuel
spraybars 51 integrally therein and cooled by bypass air. Similar
air cooled flameholders are disclosed in detail in U.S. Pat. Nos.
5,813,221 and 5,396,763 both of which are assigned to the present
assignee.
[0040] The augmenter 34 requires an ignition source or pilot in the
cases where the core gas conditions are not conducive to reliable
auto-ignition during light-offs. An augmenter swirler pilot 65 in
the turbofan gas turbine engine augmenter 34 includes a fuel/air
swirler 64 disposed between an axially extending bypass flowpath 25
and an axially extending exhaust flowpath 128. In the exemplary
embodiment of the augmenter swirler pilot 65 illustrated herein,
the fuel/air swirler 64 is mounted to the mixer wall 100 upstream
of radial flameholders 52. The fuel/air swirler 64 is illustrated
herein as being circumferentially located between a pair of the
tubular injector chutes 58. Though only one fuel/air swirler 64 is
illustrated herein there may be designs where more than one are
used.
[0041] The fuel/air swirler 64 includes a swirler inlet 66 axially
open to and positioned substantially normal to the bypass flowpath
25 to receive bypass air 26. A swirler outlet 68 of the fuel/air
swirler 64 is open to and positioned substantially parallel to the
exhaust flowpath 128. A swirl chamber 67 within the fuel/air
swirler 64 is operably disposed between the swirler inlet 66 and
the swirler outlet 68 to swirl bypass air entering the swirler
inlet 66.
[0042] The swirl chamber 67 produces swirling air 69 which swirls
about a swirl axis 70 of the fuel/air swirler 64 extending through
the swirler outlet 68 and being substantially normal to the exhaust
flowpath 128. A fuel injector 86 is used to inject fuel 75 into the
swirl chamber 67 to be mixed, swirled, and atomized with the
swirling air 69 and an igniter 88 is used to ignite the resulting
mixture of the atomized fuel 75 and the swirling air 69. The
resulting mixture of the atomized fuel 75 and the swirling air 69
is ejected, while swirling about the swirl axis 70, through the
swirler outlet 68 and into the exhaust flowpath 128. The ignited
mixture then lights off the fuel 75 injected by the means for
injecting fuel 45 into the exhaust flowpath 128 and air in the
combustion zone 44. The igniter may be a spark plug or other
sparking device for producing an electrical spark. A plasma from a
microwave generator or a gaseous torch could also be used as
igniters. The augmenter swirler pilot 65 provides a stable reacting
light-off source for the flameholders to initiate thrust
augmentation.
[0043] The exemplary embodiment of the fuel/air swirler 64
illustrated in FIGS. 5 and 6 includes an air swirler 72 within a
rounded swirler housing 82 of the fuel/air swirler 64. The air
swirler 72 is centered about the swirl axis 70 within the housing
82 of the fuel/air swirler 64. The air swirler 72 may be louvered
or have a plurality of swirling vanes 78. The swirler inlet 66 is
radially offset with respect to the swirl axis 70, as illustrated
in FIG. 8, to help the rounded swirler housing 82 impart a swirl to
the bypass air 26 entering the swirl chamber 67 within the swirler
housing 82. The air swirler 72 greatly increases the amount of
swirl imparted by the fuel/air swirler 64.
[0044] An exemplary embodiment of the air swirler 72 is a swirler
cup 90 which may be louvered or have the plurality of swirling
vanes 78. The distinction between the two is that the louvered
swirler cup has angled slits which are angled with respect to the
swirl axis 70 while the swirling vanes 78 are disposed at an angle
with respect to the swirl axis 70 in an open annulus in the swirler
cup 90 and centered about the swirl axis 70. The swirler cup 90 may
include a tilted edge 92 as illustrated in FIG. 9 or a chamfered
edge 94 as illustrated in FIG. 10. The mixer wall 100 may be
provided with a rounded lip 96, at least in the vicinity of the
swirler cup 90, which together with the tilted or chamfered edges
92 and 94 may be used to provide obscuration of the swirler cup
90.
[0045] The exemplary embodiment of the fuel/air swirler 64
illustrated herein includes an air scoop 80 leading from the
swirler inlet 66 to a rounded swirler housing 82. The air swirler
72 is disposed within the rounded swirler housing 82. The air scoop
80 has a swirler inlet sidewall 84 extending from the swirler inlet
66 to the swirler housing 82 and the swirler inlet sidewall 84 is
substantially tangentially attached to the swirler housing 82. An
exemplary embodiment of the air swirler 72 is a swirler cup 90
which may be louvered or have a plurality of swirling vanes 78. The
air scoop 80 and swirler inlet sidewall 84 increase the amount of
swirl imparted the rounded swirler housing 82.
[0046] The augmenter 34 described above improves durability of the
exhaust system as well as provides for higher thrust derivative
products by the new combination of the cooled step ring and radial
flameholders 50, 52, and injector chutes 58. The cooled
flameholders with integral fuel injection improve auto-ignition
margin, as well as reduces fuel coking and boiling. The performance
augmenter 34 provides improved efficiency during both dry and
reheat operation of the augmenter. The individual injector chutes
58 are isolated or decoupled from the step ring flameholder 50 as
described above for improving thermal durability of the step ring
flameholder 50 itself by reducing circumferential temperature
variations, as well as improved combustion stability during
light-off propagation by isolating the recirculation zone 57.
[0047] While there have been described herein what are considered
to be preferred and exemplary embodiments of the present invention,
other modifications of the invention shall be apparent to those
skilled in the art from the teachings herein, and it is, therefore,
desired to be secured in the appended claims all such modifications
as fall within the true spirit and scope of the invention.
[0048] Accordingly, what is desired to be secured by Letters Patent
of the United States is the invention as defined and differentiated
in the following claims:
* * * * *